1. Field of the Invention
The present invention relates to neutron dosimetry and more particularly, to a simplified fast neutron dosimeter utilizing a polycarbonate film and electrochemically etching the same.
2. Description of the Prior Art
A need exists for a fast-neutron dosimeter that is low in cost, easily used, small in size, tissue equivalent in composition, sensitive to neutrons and insensitive to beta, gamma, and x-rays, having a wide dose range, and being relatively insensitive to ambient conditions such as humidity and temperature, thereby having a low fading rate. To be truly practical, the device must also be capable of being easily read so that detected neutron doses may be evaluated with ease.
During the past decade a number of efforts have been made to reach these goals. In particular, track etching methods have been attempted in neutron dosimetry. One such method of neutron dosimetry using track etching techniques in personnel dosimetry has been the use of fissionable materials such as 237Np and 232Th in contact with a 10 .mu.m thick polycarbonate foil (such as KIMFOL) glued on a LUCITE "O" ring. These foils are etched in a 28% KOH solution at 60.degree. C. and the etched perforated track density is determined using a spark counting technique. This method, which involves the combination of fissionable material with plastic, has a number of advantages over earlier known proton track registration in special nuclear track emulsions; however it suffers from the disadvantage of the complexity and cost of using fissionable materials. Accordingly, simpler and more convenient techniques for use as dosimeters are still needed.
Electrochemical etching was introduced by Tommasino. The work of Tommasino was involved in the registration of fission fragment and alpha particle tracks and is described in CNEN Report RT/PROT (71), 1, 1970.
Further research in electrochemical etching was performed by the present Inventor at Oak Ridge National Laboratory wherein it was shown that large fission fragment tracks could be obtained in polyester materials (gamma film backing) by electrochemical etching in a 28% KOH solution with the application of 2000 V at 1 kHz frequency. Similar research relating to fast-neutron-induced recoil particle tracks was carried out with regard to certain other organic foils such as cellulose acetobutyrate (NTA film backing). The result of this research, however, was not considered to successfully achieve the goals set forth above of providing a truly satisfactory personnel dosimeter. Such work is reported in ORNL-TM-3605 (1971) entitled "Some Studies on the Application of Track Etching in Fast Neutron Personnel Dosimetry." In particular, the tracks observed in the cellulose foils had poor contrast and were not well defined. The lack of adequate track contrast and definition, of course, rendered the techniques under investigation of little value for commercial exploitation since the results obtained, although different in nature, were not substantially better than those obtainable by other well known prior art etching techniques.
A need was therefore seen to exist for further research and development toward the above established goals of producing a truly effective personnel neutron dosimeter as well as a dosimeter for general fact neutron dosimetry applications.